This invention relates to component installation/removal devices and improved tips for use therewith and, in particular, to hand-held devices where heat generated at the tip is produced by electrical current conducted through the tip.
In general, the devices of the present invention are typically usable with components mounted on a substrate such as a PCB where such components include surface mounted devices (SMD's) and thru-hole devices, sockets, plugs, connectors, heat sinks, etc. where the component may have leads or terminals at one or more sides thereof, it being understood that the terms "leads" and "terminals" are used interchangeably hereinafter. Moreover, in general, a substrate such as a PCB includes anything not a component such as ground and voltage planes, all circuitry, laminates, conformal coatings, board stiffeners, etc.
Component operations include removal, installation, replacement, re-positioning, adding solder, removing solder, reflowing solder, curing and/or overcuring adhesives and coatings, etc. When removing or installing certain components from a substrate in certain applications of the invention, it may be desirable to heat the leads or terminals of the component in order to melt the solder associated with the leads. In such instances, the metallized castellations of a so-called leadless chip carrier would be considered the leads or terminals of the component.
With the foregoing definitions in mind, the invention and the background thereof will now be described in terms of specific applicat.ions, it being understood, there is no intent to limit the invention to such applications. Rather, the scope of the invention extends to the wide variety of applications suggested by the above definitions and other applications which will occur to those engaged in this art.
Heretofore, as exemplified by U.S. Pat. Nos. 3,804,320 and 4,034,202, tweezer-type devices have been employed to engage the terminals at opposite sides of an integrated circuit component such as a dual-in-line package (DIP) to effect removal of the component from a printed circuit board (PCB) or the like. In these devices the tips respectively associated with the arms of the tweezer-type device are similar to soldering iron tips in that heating elements respectively disposed at the arms generate heat which is conducted to the tips. This heat melts the solder connecting the component to the board to thus facilitate installation or removal of the component. The tips disclosed in the above patents are designed to engage opposite sides of a DIP or the like. Other tips are known which are bifurcated such that each tip engages adjacent sides of the component so that both tips engage all four sides of those components having terminals at each side thereof.
The above devices have certain shortcomings in that the use of heat conducting tips of the type typically used in soldering irons or the like are relatively thick at the distal ends thereof and thus it is difficult to insert such tips between closely spaced adjacent components without subjecting an adjacent, good component to the possibility of damage. In particular, the solder joints of an adjacent component should not be crystallized by the application of heat to a component being replaced or installed since such crystallization impairs the electrical connection effected by the solder joint.
Accordingly, it is a first object of the present invention to provide an improved component removal/installation device having an improved tip which can more readily be inserted between closely spaced adjacent components. For example, Plastic Leaded Chip Carriers (PLCC) are presently spaced as close as 20 mils apart. Thus, it is an object of this invention to provide improved tips which can be readily inserted between adjacent PLCC's or the like without damaging the adjacent component.
Another shortcoming associated with the prior art devices is that the heat is not generated at the point where it is needed--that is, at the terminals of the component. Thus, in soldering iron-type devices, the heat is produced in a coil or the like substantially removed from where it is needed and transferred via the tip to the solder to be melted which results in heat loss and inefficiency of heat utilization.
Accordingly, it is a further object of the invention to provide an improved component installation/removal device where the heat is produced precisely where it is needed thus providing efficient heat generation.
Another problem associated with the soldering iron tips of the prior art is that they are relatively massive and hence heat tends to radiate therefrom. This radiated heat tends to raise the temperature of the adjacent solder joints and thus for this further reason the tips of the prior art devices are undesirable.
Accordingly, a further object of the invention is the provision of a improved component installation/removal device utilizing an improved tip wherein heat radiation from the tip is minimized.
Another shortcoming associated with the tips of the prior art devices is also related to the relatively massive character of the tips. That is, as described in copending Application entitled "Component Adaptable Heating Devices for Removing and Installing Components With Respect to a Substrate and Improved Control Circuitry for Use Therewith" having Ser. No. 07/395,073 and filed Aug. 17, 1989, now abandoned, and assigned to the assignee of the present application (the foregoing application being incorporated herein by reference), it is desirable to controllably raise the temperature of the component or its terminals. However, due to the high temperature (typically above solder melt temperature and the large thermal mass of soldering iron-type tips, heat can not be controllably transferred to the component terminals. Rather, heat transfer occurs rapidly and in an uncontrolled manner such that not only the component is subject to thermal damage but adjacent components and their soldered joints are also subject to such damage. This thermal damage may include overheating, thermal shock, and other types of thermal degradation.
Accordingly, it is a further object of the present invention to provide a device and improved tip which avoids thermal damage and unwanted heating and crystallization of adjacent solder joints often associated with soldering iron-type devices, or with unfocused hand-held hot air reflow devices, where the thermal mass and/or material of the improved tip is such that the tip may be heated in a controlled manner and subsequently cool down rapidly.
In particular, it is a further object of the present invention to provide small, low mass tips which can fit into tight, hard-to-reach places to engage the terminals of a component to be installed or removed, and which allow a relatively unobstructed view of and access to the component from the top - that is, "z-axis" viewing and access. Upon application of electrical current to the tip, the temperature of the terminals is increased at a controlled rate to at least solder reflow temperature. After solder reflow, the tip (which may be tinnable or non-tinnable) continues to engage the component leads. Accordingly, installation or removal of surface mounted devices (SMD's) can be effectively implemented. The controlled temperature ramp-up not only minimizes thermal shock or other thermal damage to sensitive components, but also drives off solder paste volatiles before solder melt, thereby reducing the chance of solder ball formation and spattering.
As stated above, the tips may engage the terminals of a component. In particular, in accordance with a further object of the invention, the tips may have various configurations including those adapted to grasp the terminals of J-leaded or leadless type components or to clamp the gull-wing leads of a flat pack or the like.
Moreover, it is a further object of the invention that the tips be provided with a tinnable layer to thus effect a soldering iron device or the like wherein heat generation occurs within the tip due to the passage of electrical current therethrough, the heat then being transferred to the tinnable layer. Thus, heat generation occurs in the tip rather than in a coil or the like far removed from the working end of the tip as is the case with conventional soldering irons.
It is still a further object of the present invention that the tips be provided with a variety of sheathing or overlayer combinations to achieve various application requirements. One such combination would consist of an electrically-insulative, heat-conductive, non-tinnable sleeve which would effect heat transfer from the tip to the work yet prevent any leakage current produced by the tip from passing to sensitive components or board circuitry thereby preventing any possible damage. Such an electrically-insulative sleeve or overlayer could either consist of a compliant material such as fiberglass braid or wrap, or a non-compliant or rigid material such as a ceramic compound; however the compliant material would have the additional advantage of facilitating good tip-component or tip-component lead contact and thus, good heat transfer.
In accordance with a further object of the invention, an alternative sheathing or overlayer combination may include one of the above mentioned electrically-insulative, heat-conductive sleeves with an additional metallic overwrap covering this sleeve, which would, in turn contact the component or component leads. This metallic overwrap may either be tinnable or non-tinnable and compliant or rigid (or any combination thereof) and would also serve to make the tip more wear or abrasion resistant than a tip with the electrically-insulative sheathing alone.
Moreover, in accordance with a preferred embodiment of the invention, the foregoing metallic overwrap may be provided in various configurations to thereby effect selective contact and heat transfer to a variety of components with the same basic tip.
A further shortcoming with the prior art devices and, in particular, those devices which have bifurcated tips to facilitate engagement with all four terminal sides of a component is that, due to the rigidity of the tips and the fixed orientations thereof with respect to the tweezer arms, the registration thereof with respect to the component terminals must be essentially perfect in order to ensure good thermal contact with the terminals at each side. To ensure such registration is difficult and expensive.
Accordingly, another object of the invention is to provide an improved tip capable of easily establishing a good thermal contact with the terminals along the length of each side of an integrated circuit component or the like to thus facilitate removal or mounting of the component with respect to a printed circuit board or the like.
These and other objects of the invention will become apparent from a reading of the following specification and claims taken with the drawing.